one girl's diary of improvisational engineering

Espresso Machine Sous-vide

This project is a bit different from what I normally do. No firmware to write, just several trips to the hardware store and a lot of quality time with the drill, files, and nibbler. But this one has a higher purpose: Food.

It was actually a commission by a friend of mine. He wanted to try sous-vide cooking, but neither of us were crazy about the idea of paying for something lab-grade, and even the consumer-focused SousVide Supreme seemed kind of lame with its $450 price tag and no circulation pump.

The easier solutions (like a modified crock pot) didn’t seem to meet my friend’s requirements. He wants the flexibility to use large water baths sometimes, and he wants it to be stable for long durations. So, a real immersion circulator starts to sound awesome for this. I was really close to building the Seattle Food Geek DIY circulator above, when I noticed one of his ideas for improving the design:

“After burning out my first set of heating coils, I realized that there must be a better method of heating the water. The coils are very effective and heat the water very quickly. However, I’m pretty paranoid about burning them out again, and they’re a pain to replace. I’ve found some commercial immersion heating elements, but they’re about $100, which inflates the budget for this project by quite a bit. I may try using the heating element and pump system from an old espresso machine, the kind that makes steam. Since it already has a self-contained heater and an pump, it might even be cheaper than the heating coils and aquarium pump.”

Well, this is what I ended up doing. I’m not sure it ended up being cheaper (those heating coils he used were really cheap!) but it was definitely fun to build, and the end result is working pretty well:

This turned out to be a really interesting design, because you can use it with nearly any water bath vessel. Even the lab-grade immersion circulators need a place for the circulator to stick out on top, and this often means making a custom lid. I usually use this machine with a small icechest, but I’ve also heated up water in plain soup mugs and mixing bowls. You just run three hoses in (inlet, outlet, and temperature probe) and you’re set. Of course, the more insulation you have, the easier it will be to keep the temperature steady.

On the downside, this design can take a while to heat the water. I think it took maybe 30 minutes to heat about a gallon of room-temperature water up to 140°F. This is certainly not limited by the heating element- the espresso machine heater is 1200 watts. However, I have a mechanical thermostat on it that keeps the heating element from rising too far above 120°C. It’s okay if we make a little bit of steam, but it’d be bad if the steam got too hot. So what ends up happening, is that while you’re initially heating the water, the PID is telling the heating element to run at full power, but the mechanical thermostat is still keeping it from overheating. So when you’re initially heating the water, our limiting factor is the pump’s flow rate. If it’s too slow, the inlet water isn’t coming through fast enough to cool off the heater.

I spent what seems like a week shopping for alternative pumps. I looked through McMaster-Carr, eBay, even tried a CPU water-cooling pump. That one was nicely high flow-rate… until you give it any sort of load, that is. And to be practical, this design really needs a self-priming pump. So, I stuck with the one that came with the espresso machine. It’s not actually that bad. The only tweak I had to make is to limit the pump’s power using a ceiling fan speed controller. Since it’s a solenoid type pump, this only limits the strength with which the solenoid slams from side to side. The actual flow rate is mostly fixed, since the solenoid is oscillating at your mains frequency. The reduced power helps the pump run much quieter and cooler, which is rather necessary when you’re running something continuously that wasn’t meant to.

Since assembling this thing, my boyfriend and I have cooked several meals in it. As long as we’re patient enough to let the PID loop fully settle before cooking anything, it’s remarkably accurate. I can routinely hold the water bath within 0.4 °F or so. Of course, sometimes the PID goes nuts and overshoots/undershoots too. I’m sure I’ll get more feedback on this once I deliver it to my friend 🙂